The invention relates to circuit arrangements for measuring currents at high potential in general and more particularly to such an arrangement which utilizes a light emitting diode.
Circuit arrangements consisting of a measured value generator with a capacitor which is charged by a current proportional to the current to be measured and is discharged via a parallel connected light emitting diode when a defined voltage is reached to generate a sequence of light pulses with frequency proportional to the current to be measured, which sequence is transmitted, via an optical transmission path, to a measurement value receiver with a photo element, are known. In one known circuit arrangement of this type (German Auslegesschrift No. 15 91 972), a four-layer diode, which becomes conducting when the defined voltage at the capacitor is exceeded, is connected in series with the light emitting diode, so that a discharge current flows in the branch parallel to the light emitting diode. This discharge current excites the light emitting diode to emit light. Due to the discharge, the capacitor voltage drops, so that the parallel branch finally ceases to conduct. The capacitor is thereupon charged again, the shunt branch becomes conducting and a new light pulse is generated. The number of light pulses delivered per unit time is therefore proportional to the current to be measured.
It is a particular disadvantage of the known circuit arrangement that its dynamic range and therefore, its measuring range, is limited by the firing and holding current of the four-layer diode.